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CO is a colorless, odorless and tasteless gas, so a high concentration in air is undetectable by humans. It does not cause irritation, but because of its molecular weight similar to that of air, it mixes and travels freely into the airways with inspiration. As a consequence, it reaches the bloodstream and combines with hemoglobin in the blood, causing carboxyhemoglobin. This results in the loss of its ability to carry oxygen through the body, preventing the supply of oxygen to cells through respiration.
CO is usually produced in incomplete combustion of oil, gas and wood, among others. It is considered a neurotoxic substance that poses a risk of serious health effects in case of prolonged exposure by inhalation. Toxic effects can occur on both the central nervous system and the auditory system.
The WHO establishes recommended concentration limits in outdoor areas. A limit of 25 ppm is determined for exposures in one hour, and 9 ppm for exposures in an 8-hour working day. The daily environmental exposure limit value (ELV-ED) establishes a maximum of 20 ppm in Spain. The limit value for human health protection is also 9 ppm for an 8-hour working day. With respect to indoor exposure limits, LEED certification establishes a limit of 9 ppm in a pre-occupancy air test of new construction.
Based on the recommended values mentioned above, the following ranges of indicators are established:
The measurement of CO concentration in the air can be done either in ppm (parts per million) or in mg/m3. Although MICA collects the values in ppm, a conversion to mg/m3 can be made, considering the conditions of the indoor environment. For a temperature of 20 ºC, the conversion to be used is as follows:
- 1ppm ~ 1.165 mg/m3
CO is mainly produced outdoors by the incomplete combustion of fuels such as oil, wood, natural gas, charcoal and kerosene. These combustions occur mainly in industry and traffic. In addition, there are also indoor emissions due to incomplete combustion such as from gas stoves, gas stoves, boilers or fireplaces. Tobacco smoke is also an important source of emissions.
High concentrations of CO in the air are hazardous to health because, being a colorless, odorless and tasteless substance, it is imperceptible to humans until the onset of symptoms. When a space is free of CO, inhalation is prevented and, as a consequence, the formation of carboxyhemoglobin in the bloodstream is prevented. Thus, oxygen combines with hemoglobin without major difficulty, facilitating its transport and the oxygenation of all organs and tissues of the body.
CO is included in the ISTAS blacklist due to its classification as neurotoxic level 4. These toxicity effects are mainly linked to the central nervous system and the auditory system. This toxicity occurs by inhalation. In addition, it may cause adverse effects on fetuses during pregnancy.
In low concentrations, may cause fatigue or chest pain in people with heart failure. In moderate concentrations it may cause angina, impaired vision and reduced brain function. At very high concentrations, it may cause coordination failure, headache, confusion, nausea, loss of consciousness or even death if exposure is prolonged.
